Plant-based nanostructured silicon carbide modified with bisphosphonates for metal adsorption

Abstract

Nanostructured silicon carbide possesses superior properties such as excellent hardness, high chemical stability, large surface area and good sintering ability at relatively low temperatures compared to bulk silicon carbide. However, its synthesis with conventional methods is still challenging. In the present study, we produced nanostructured silicon carbide from barley husks with a simple self-propagating high-temperature synthesis. Barley husks were chosen as the raw material because they are agricultural residues widely available and contain large amount of nanostructured silica suitable as a precursor in the synthesis. We studied the effect of two processes to valorize the barley husks on the extracted silica particles: burning in an industrial scale furnace to produce heat energy and pyrolysis to extract organic compounds as well as controlled calcination as a reference. The processing prior to the extraction affected morphology and composition of the nanostructured silica. The highest purity and surface area of 187 m2/g was obtained for the silica extracted from pristine barley husks through calcination. On the other hand, pyrolysis allows additional valorisation of the biomass by producing bio-based organic chemicals and still the silica particles with relatively high surface area, 105 m2/g, can be extracted. Nanostructured silicon carbide was produced from the extracted nanostructured silica with magnesiothermic reduction via self-propagating high-temperature synthesis. Nanostructured silicon carbide produced from silica particles undergone calcination had the highest surface area of 196 m2/g. Furthermore, it was functionalized with bisphosphonates to be used as a metal adsorbent and examined in adsorption of manganese from landfill water with pH 8. The functionalization of the silicon carbide with bisphosphonates increased the adsorption capacity by 32 % and the material was able to withstand at least 5 adsorption/desorption cycles.